1. Field of the Invention
The present invention relates to a method for identifying double-layer disc and an optical disc apparatus.
2. Description of the Related Art
In recent years, there are many varieties of optical discs including DVD-based discs of high-density recording such as DVD-ROM, DVD±R, DVD±RW, etc. which have been increasingly developed and made commercially available as well as conventional CD-based discs such as CD-ROM, CD-R, CD-RW, etc. Furthermore, multilayer discs for improving memory capacity of one disc, double-layer discs in general, have been proposed in various occasions. In particular, a double-layer DVD-ROM has already been made commercially available.
Under the circumstances, an optical disc apparatus into which various discs are loaded is required to be compatible which can correspond to these various discs by itself. For example, an optical disc apparatus capable of handling DVD-based optical discs is required to be able to record and reproduce CD-based discs as well as DVD-based discs.
It is constitutionally necessary for a compatible-type optical disc apparatus to identify the type of optical discs loaded into the optical disc apparatus prior to recording and reproducing because recording and reproducing method or the conditions (parameters) of information differ many times depending on the type of optical discs.
The conventional art relating to this kind of disc identification include an identification technique which discriminates a DVD-based disc between recordable disc, rewritable disc and ROM disc based on the reflectance since reflectance of single-layer ROM disc and single-layer recordable disc are 45% or more and the reflectance of double-layer ROM disc and single-layer rewritable disc are 18% or more and 30% or less, for example.
Conventionally, disc type identification has been performed by drawing focus at a CD wavelength and looking at RF signal level. When the reflectance is high (45% to 60%), a disc is identified as a CD-ROM or a CD-R and when the reflectance is low (15% to 30%), it is identified as a CD-RW and it is further reconfirmed as CD-based or not by looking at S-curve with more tracking. However, it takes time to identify a CD-R or a CD-ROM, because it is necessary to perform further recording or to verify presence or absence of wobble. If it is identified as non CD, DVD identification will take place. DVD-ROM includes a single-layer medium having only a first layer and a double-layer medium having two layers of first and second layers. It is possible to discriminate from the reflectance alone when DVD-ROM is a single-layer medium because only first layer of the single-layer medium has a high reflectance (45% to 60%). However, the reflectance of the first and second layers of double-layer DVD-ROM are the same as double-layer DVD±R or DVD±RW medium and it is impossible to discriminate from the reflectance alone. Therefore as similar to CD, it is identified as a DVD-R or DVD-RW by performing a recording, etc. after it has been identified as DVD from presence or absence of wobble or by looking at S curve with further tracking and the process takes a long time.
Furthermore, a method for identifying disc types comprehensively based on the signal information after obtaining all the signals of reflection, focus error and tracking error based on the reflective light of each laser beam irradiated once from the laser beam sources for CD and DVD mounted on an assumed compatible optical disc apparatus is proposed in Japanese Patent Application Laid-Open (JP-A) No. 11-306650.
Moreover, a method for identifying which contain a step of operating a focus servo, a step of obtaining tracking error signal of push-pull type from optical discs, and a step of identifying optical disc types such as DVD-RAM, DVD-RW or DVD+RW, for example, by comparing amplitude of tracking error signal with a predetermined value is proposed in JP-A No. 2002-312933. Or a method of using frequency of wobble signal is also proposed in JP-A No. 2002-312933.
However, in the method disclosed in JP-A No. 11-306650, identification of double-layer disc is not assumed, there is no way to discriminate between double-layer DVD discs such as DVD-ROM, DVD±R and DVD±RW and the identification process is complicated because it is comprehensively decided based on the reflection signal, focus error signal and tracking error signal, etc.
On the other hand, in the method disclosed in JP-A No. 2002-312933, discriminating between DVD-RAM and DVD±RW is performed based on the frequency of push-pull signal or wobble signal and it is effective for discriminating between single-layer DVD disc and double-layer DVD ROM. However, it is impossible to discriminate between double-layer DVD discs such as DVD-ROM, DVD±R and DVD±RW.